This proposed research should lead to development and characterization of a semi-preparative scale Supercritical Fluid chromatograph (SFC) optimized for purifying combi-chem libraries and offering up to 2 orders of magnitude increase in throughput over traditional preparative HPLC. This would make it economically feasible to purify entire combi-chem libraries, leading to fewer false positive and false negative screening results. SFC purification is far more productive than preparative HPLC with parallel columns. Not only do SFC separations take approximately 1/10th the time of HPLC, but SFC dramatically accelerates solvent removal from separated fractions by removing the need for lyophilization, and eliminates generation and disposal of vast amounts of mixed aqueous/organic waste. Preliminary testing of a prototype system show that the system is capable of purifying 200 samples per day with solute quantities of 1-100 mg, with better than 95% recovery and purity. The gas/liquid separator design allows for collecting multiple fractions per sample, enabling recovery of not only reaction products but also of scarce unreacted starting materials in a highly purified state. The focus of this research is to optimize and characterize the system for a diversity of drug discovery compounds, and demonstrate feasibility of integrating this system with a robotic fraction collector. PROPOSED COMMERCIAL APPLICATIONS: The proposed Semi-prep SFC system, when fully automated with a laboratory robotic system, should eliminate a major bottleneck in the drug discovery process and allow for purification of entire combi-chem libraries on a scale not economically feasible with current HPLC technology. This will result in combi-chem libraries far more likely to yield positive hits associated with a known pure chemical entity.